The most common site for extra-intestinal Escherichia coli infection is the urinary tract. There are a number of risk groups for this site of infection, one of which being young women in their sexually active years. Infection in this group accounts for 6-7 million office visits annually in the United States. Escherichia coli isolates are responsible for greater than 80-90% of these episodes. About 250,000 of these infections progress to acute pyelonephritis. In approximately 20% of these women frequent recurrences of infection (3-6/annum) follow the first episode. The morbidity, time lost from work of cost of infectious syndrome is considerable. An improved understanding of the pathogenesis of this disease would be of significant importance. It is believed that the vast majority of recurrent UTIs are episodes of reinfection with different strains of E. coli rather than persistance of a single strain. We are employing pulse field gel electrophoresis to generates DNA "fingerprints" of bacterial strains isolated from women with recurrent UTIs. This will allow use to definitively establish how frequently a single strain versus different strains are responsible for this pattern of infection. Our studies to date on isolates from eight women suggests that infection from a single strain my occur more frequently than is presently suspected. If a single strain is responsible for the majority of recurrent UTIs our therapeutic approach in this subset of women will be altered. Several possibilities could account for the above findings. We plan to genotype serially collect isolates from a larger number of women with recurrent UTIs. This will confirm the above findings, we also plan to genotype fecal isolates from these women that were collected in between and during infectious episodes. This data should clarify whether the responsible strain was persisting within the gastro-intestinal tract or within the urinary tract.